1. Field of the Invention
The present invention relates to mode switch control apparatus and method for a hybrid transmission and, more specifically, relates to the mode switch control apparatus and method for the hybrid transmission which are capable of smoothly performing a mode switch (or mode transfer) from a low mode which is suitable for a continuously variable transmission (or called, an infinitely variable transmission) in a low shift (gear) ratio area to a high mode which is suitable for the continuously variable transmission in a high shift (gear) ratio area without an output torque variation and discontinuity of a change in the (gear) shift ratio.
2. Description of the Related Art
A Japanese Patent Application First Publication No. 2000-62483 published on Feb. 29, 2000 (which corresponds to a U.S. Pat. No. 5,931,757 issued on Aug. 3, 1999) exemplifies a previously proposed hybrid transmission. In the previously proposed hybrid transmission, a differential unit mutually links an engine, an output axle, and motor/generators and a clutch to mutually couple first predetermined revolutional elements constituting the differential unit and a brake fixing second predetermined revolutional elements are installed, these clutch and/or brake selective engagement operation selectively constitutes the low mode which is suitable for the continuously variable transmission in the low side shift ratio area and the high mode which is suitable for the continuously variable transmission in the high side shift ratio area. However, a mode switch technique between the low mode and the high mode has not specifically been proposed. Hence, when the mode switch in the previously proposed hybrid transmission is carried out, it is a common sense that, when it becomes a driving state to perform the mode switch, the corresponding clutch and/or brake is in an engagement state from a release state or, on the contrary, in the release state from the engagement state.